Toxicity And Filed Control Efficacy Of Metaflumizone And Its Mixtures Against Spodoptera Frugiperda

The fall armyworm,Spodoptera frugiperda（J.E.Smith）（Lepidoptera:Noctuidae）,is an important agricultural pest native to the Americas.S.frugiperda is characterized by wide host range,rapid migration and diffusion,strong reproductive ability,wide suitable area,severe sudden damage and high resistance level to some insecticides.S.frugiperda has developed a high resistance to insecticides including organophosphorus,carbamate,pyrethroids,spinosad,diamides and macrolides insecticides because of long-term and irrational chemical insecticides usage.In addition,S.frugiperda has also developed a high resistance to some Bt toxins in transgenic corn.The fall armyworm,which has invaded into China,carries resistance genes to the traditional pesticides.In addition,moderate levels of resistance were also developed to the recommended control agents emamectin benzoate and chlorantraniliprole,indicating a high risk of resistance in the invaded S.frugiperda.Therefore,it is vital to screen new insecticides for the sustainable control of S.frugiperda.Metaflumizone belongs to the semicarbazones insecticides,which has good control efficacy on Lepidopteran larvae in different instars and low toxicity to the mammals and aquatic organisms.Metaflumizone has been registered for control of S.frugiperda in its native region of the Americas.However,there has no studies on the control of metaflumizone against S.frugiperda in China.Therefore,this study compared the toxicity level and field control efficacy of metaflumizone and other commonly used pesticides against S.frugiperda.At the same time,a synergistic effect with metaflumizone and other pesticides including compound formulation and mixing ratio was studied.Last,the insect detoxification metabolism was preliminary explored in laboratory.The results provided the theoretical basis for scientific application of metaflumizone for the control of S.frugiperda.The main results are as follows:1.Metaflumizone has good insecticidal activity and field control effect against S.frugiperdaThe toxicity levels of metaflumizone and emamectin benzoate,chlorantraniliprole,indoxacarb and lufenuron against S.frugiperda were determined by diet-incorporated method.The control efficacy of 22%metaflumizone suspension concentrate,5.7%emamectin benzoate water dispersant and 150 g/L indoxacarb suspension concentrate in field was determined by artificial spray approach.Laboratory bioassay results showed that metaflumizone had insecticidal activity against the 3rd and 6th instar larvae of S.frugiperda,and the LC₅₀s were 2.64 mg/kg and 4.36 mg/kg,respectively.Especially the insecticidal activity of metaflumizone is second only to emamectin benzoate against the sixth instar larvae.The LT₅₀s of metaflumizone and control against 3rd instar larvae of S.frugiperda were measured at their respective LC₉₀ concentrations.The result showed that LT₅₀s of metaflumizone and indoxacarb were less than 12 h,which were less than the LT₅₀ of emamectin benzoate,lufenuron and chlorantraniliprole,indicating that metaflumizone had the characteristics of quick action against S.frugiperda.The field efficacy test showed that metaflumizone had a good control effect on S.frugiperda at the minimum recommended concentration of 6.6 g/667m²,and the relative control effects of metaflumizone were 47.67%,61.71%and 66.92%,at the first,third and seventh days,respectively.And the control efficacy was no significant difference between metaflumizone and indoxacarb,which at the recommended dosage of 2g/667m².The relative control effects of metaflumizone at the highest recommended dose of 17.6 g/667m² on day 1,3 and 7 were 69.97%,78.98%and 82.86%,respectively.The control efficacy was no significant difference between metaflumizone and emamectin benzoate,which at the recommended dose of 1g/667m².2.The combination of metaflumizone and Empedobacter brevis has synergistic effect on the control of S.frugiperdaThe toxicity level of the combination of metaflumizone and spinosad was determined by diet-incorporated method,and the toxicity level of the combination of metaflumizone and E.brevis was determined by leaf immersion method.The bioassays showed that the combination of metaflumizone and spinosad only had additive or antagonistic effect,while metaflumizone and E.brevis had synergistic effect at 9 mass ratios ranging from 1:1.28 to 1:104.26,and the cotoxicity coefficients were all greater than 120.The synergistic effect was most obvious when the mass ratio was 1:4.96,and the cotoxicity coefficient reached at 219.28.The results of field efficacy test showed that the combinations of E.brevis,which dose was half of the recommended dose of120 m L/667m²,and metaflumizone which dose were reduced by 25%and 50%of the recommended of 80 m L/667m²,respectively.And after 7 days treatment,the relative control effects of the combinations were 92.65%and 80.91%,respectively.There was a significant difference of the control effect between the combinations and the recommended dose of E.brevis,which control effect was 62.82%.While there was no significant difference between the combinations and recommended dose of metaflumizone,which control effect was 86.48%.When the dosage of E.brevis was reduced by 50%,and the dosage of metaflumizone was reduced by 75%,the relative control effect of the combination was 70.09%after 7 d application.And the control effect was no significant difference between the combination and the recommended dose of E.brevis and metaflumizone.It follows that the combination of metaflumizone and E.brevis can achieve the goal of reducing the use of chemical pesticides without reducing the control efficacy.In a conclusion,the combination of metaflumizone and E.brevis has synergistic effect against S.frugiperda.3.Glutathione-S-transferase and carboxylesterase participate in the detoxification metabolism of metaflumizone by the larvae of S.frugiperdaThe activities of multifunctional oxidase（MFO）,glutathione-S-transferase（GST）and carboxylesterase（Car E）in the 3rd instar larvae of S.frugiperda treated with metaflumizone at different concentrations for 72 h were measured by enzyme-linked immunosorbent assay.The results showed that the MFO activity in the 3 treated groups were 1.07,1.41 and 0.96 IU/mg pro at the concentrations of LC₁₀,LC₅₀and LC₉₀,respectively,and there was no significant difference or significantly decreasing of the MFO activity between the treated groups and the control group,which MFO activity was 1.16 IU/mg pro.It was showed that the GST activity were 0.14,0.16 and 0.09IU/mg pro,at the same concentrations of metaflumizone,respectively,which were significantly higher than that of the control group（0.07 IU/mg pro）.And the GST activity was the highest at LC₅₀,which was 2.32 times than that of the control group.The Car E activity were 0.32,0.38 and 0.52 IU/mg pro in the 3 treated groups,respectively,which were significantly higher than that of the control group at 0.17IU/mg pro.The highest Car E activity was 3.01 times than that of the control group.Therefore,it was speculated that GST and Car E were involved in the detoxification metabolism of metaflumizone by S.frugiperda.